At the present time the ozonization process which ensures the disinfection of water is applied with the aid of two contact vessels or tanks which are arranged in series. The purpose of the first contact tank is to respond to the chemical demand of the water for ozone and to establish a predetermined ozone content (C), for example 0.4 mg/l, at the entry of the second contact tank. The purpose of the second contact tank is to make it possible to maintain the ozone content established at the entry for a time (T) necessary to obtain the disinfection conditions which it is desired to apply (C.times.T=a required value).
Recent investigations carried out into the action of ozone as an oxidizing agent have revealed two actions of ozone: direct oxidation and radical oxidation. In this connection reference may be made to the French certificate of addition 8817134 (U.S. Pat. No. 2,640,957). Furthermore, modern means of analysis have made it possible to investigate the oxidation kinetics and to demonstrate two types of reaction kinetics: fast reactions which take place with short reaction times, measured in a second, and slow reactions which take place with long reaction times, measured in minutes.
It is known that the radical action can be intensified by introducing a promoter for the production of OH radical, for example hydrogen peroxide, ultraviolet radiation etc. (a process called "Perozone" developed and improved by the companies Lyonnaise des Eaux Dumez and Degremont). The hydrogen peroxide is generally introduced either at the head of the two contact tanks or at a point situated between the two tanks.
Operating in this manner has the disadvantage that the hydrogen peroxide reacts with the ozone in the water, making it disappear. As a result of this it is impossible to implement the control of the quantity of ozone to be produced and injected into the two contact tanks respectively, this control being conventionally performed by measuring the ozone in the water while at the same time taking into account the variations in the flow rate being treated and in the quality of the water to be treated.
The present invention proposes to optimize the ozone injections as a function of all the abovementioned factors, while eliminating the disadvantages of the previous solutions emphasized above.
The subject of the invention is therefore a reactor for the optimized ozonation of water intended for human consumption, in which the direct oxidizing action of the ozone is supplemented by the radical oxidizing action of the ozone, the latter being intensified by the introduction of hydrogen peroxide, characterized in that it comprises three contact tanks arranged in series:
a first contact tank receiving the water to be treated and intended for the direct and rapid oxidizing action by the ozone which is introduced into the said tank and brought into contact with the liquid to be treated; PA1 a second contact tank intended to ensure the disinfection of the liquid and into which is injected the quantity of ozone necessary to maintain in the liquid to be treated the ozone concentration necessary for the disinfection of the water; and PA1 a third contact tank intended to ensure the radical action of the ozone, into which there is injected, besides the ozone, a quantity of hydrogen peroxide intended to increase the quantity of OH radicals available for the reaction with the pollutants to be removed by oxidation, the treated water being discharged from this third tank.
According to the present invention the first contact tank is provided with a regulating system making it possible to control the quantity of ozone to be injected into this tank by measuring the ozone concentration in the liquid to be treated which is necessary for the disinfection, this measurement being performed with the aid of a sensor positioned at the exit of the said first tank.
According to a characteristic of the present invention, the second contact tank comprises a system for controlling the quantity of ozone to be injected into this tank, this control being carried out by measuring the ozone at the exit of this tank with the aid of a sensor, the contact time (T) in the said second tank being determined so that the product of ozone content (C).times.(T) is equal to the required value.
According to a third characteristic of the present invention the third contact tank comprises a first system for controlling the injected quantity of ozone proportionally to the flow rate of the liquid to be treated, this control system being control-driven by a sensor measuring this flow rate, and a second system for controlling the injected quantity of hydrogen peroxide, which is a function of the flow rate of liquid being treated, this control system being control-driven by the said sensor, so that the mass ratio of hydrogen peroxide/ozone is maintained at a predetermined value.
According to the present invention each of the contact tanks or any one thereof may comprise means for partitioning such as especially partitions, baffles and the like, their number and arrangement being chosen so as to allow plug flow through the tank in question to be established.